This invention relates to an ignition timing controller for an internal combustion engine. More particularly, it relates to an ignition timing controller which can prevent thermal damage to the ignition system when the engine is rotating at a low speed.
The cylinders of an internal combustion engine are ignited by spark plugs which are supplied current by an ignition coil. In many conventional ignition systems, the supply of current to an ignition coil is started at a prescribed, constant first piston position for each cylinder (such as 75.degree. BTDC) and then cut off at a prescribed second piston position which varies with the rotational speed of the engine. Normally, the second piston position occurs earlier as the engine rotational speed increases. This means that the ignition coil conducts for more degrees of crankshaft rotation at low engine speeds, such as when the engine is cranking, than at high engine speeds. Since it takes longer for the crankshaft to rotate by 1 degree at low engine speeds than at high ones, the length of time for which the ignition coil conducts may be considerably longer at low engine speeds than at high engine speeds. The electric current passing through the ignition coil and other parts of the ignition system for long periods at low engine speeds can result in their being thermally damaged.